In this section, for clarity of presentation, we illustrate how a specific ROM closure model (i.e., the D2-VMS-ROM outlined in Section ) increases the ROM accuracy for the 2D flow past a circular cylinder [1]}, which is a simple test problem commonly used in the ROM community.
(We note, however, that the D2-VMS-ROM was successfully used for challenging test problems, e.g., turbulent channel flow [2]} and the quasi-geostrophic equations [3]}.)
In our numerical investigation, we use a Reynolds number \(Re=1000\)  and four ROM basis functions (i.e., \(r=4\) ).
Details of the computational setting can be found in [1]}.
